Out of over 13,000 requests, only 2 were denied, which is less than 0.0002%. After 9/11, approximately 3% were denied, which is quite a jump, IMO. If anything, after our country was attacked and 3,000 of our citizens incinerated, you'd think the court would approve MORE of these requests, not LESS...
There are two possible conclusions from your data. One possibility is that the court became more strict after 9/11. The other is that the agencies tried to push the court further to see what they could get away with. Offhand, the second one seems more plausible.